One consequence of urban growth is the need for parking structures. As the cost of land increases, single level parking lots at grade level become less affordable, and multiple-level parking garages become the rule. Expenses for this purpose are grudgingly allowed, and they have developed as minimal structures with little or no aesthetics. The ceiling clearances are low, often only 7 feet high, and obstructions by way of beams and columns further add to a feeling of oppressiveness. Adding to this the "Hollywood" concept of a parking structure where bad events occur in the shadows, many persons become uneasy when using these structures, especially at night.
Often, conventional industrial area, and street light fixtures are used to illuminate these structures. Because such fixtures are either very simplistic, or are designed for different applications, the consequence of their use is a structure which when illuminated has many shadows and dark regions. The place becomes something of a cave, and indeed lacks some features which whether they would make it a safer place or not, at least would make a person feel more secure and likelier to want to be there.
In addition, for safety's sake, it is better for the illumination means not to glare into the eyes of the driver. Such glare can reduce the sensitivity of the driver's eyes to persons or objects in the vehicle's path, and could lead to potentially dangerous circumstances. Where luminaires are used which are not properly cut off, such glare is regularly produced.
To complicate matters, a parking structure inherently involves two sets of requirements, whose objectives are quite different. Yet these ought to be met by a single luminaire to minimize expense and clutter.
A conventional parking structure includes a central driving lane from which parking stalls branch off, usually at an oblique angle, but sometimes at a right angle, on both sides of the driving lane. For the driving lane, the objectives are, or should be, to provide a brightly lighted path along the driving lane, without glare in the eyes of the driver. Thus a symmetrical illumination pattern along the driving lane is called for, together with a cutoff of light at an angle that is sufficiently low to keep direct rays out of the driver's eyes. Side illumination into the parking stalls is of lesser importance for this path.
For the parking stalls, the criteria are quite different. Here the concept of perception becomes significant. A woman approaching her car would like to look into its backseat and find it well-enough illuminated to see that it is safe. Also, there should be no more than minimal shadows around the front and sides of the car so the person is not fearful of what may be hidden at the front end of the car.
For the parking stalls, there is little interest in illumination along the driving lane, but there is much interest in illumination of the axes oblique to it. Thus, the extent of asymmetry in the direction of the driving lane and in the direction lateral to it should be quite different from one another.
In fact, downward illumination of the two regions not only requires asymmetry along a pair of obliquely related axes, but also in more than one horizontal plane. The control of a downwardly-directed pattern is a well-known objective in area and pattern lighting. For example, see Wayne W. Compton et al U.S. Pat. No. 4,041,306 wherein illumination of specific sidewalk areas, and cut off of glare light, are objectives. However, the use of luminaires of this general class, while very adequate to direct light onto the ground in a specific pattern, attend primarily to downward illumination of the type used to light sidewalks and parks. The more sophisticated luminaires of this class are also concerned with cut off to reduce glare and visual pollution by glare light. While they do these well, their design frustrates the general type of three dimensional space illumination which is also needed to meet the objectives of this invention.
In order to provide for a feeling of security, as well as to provide illumination which reduces shadows and dark places, there is also needed a generally upward illumination that does not glare at the drivers, and that reaches well beyond the limits of the downwardly beamed light.
Along the driving lane, a generally diffuse beam directed toward the ceiling is useful for this purpose. Along the parking stalls, a more clearly regulated beam is directed toward the farther end of the stalls, together with a substantial illumination of the ceiling. These provide a substantial "volumetric" illumination along the parking stalls by both light reflected from the ceiling, and directed light.
Because of space and expense limitations, these features must all be provided in one luminaire, and this invention accomplishes that objective.